1. Field of the Invention
The present invention relates to a wireless communication device, and more particularly, to a wireless communication device used for communication with a reader/writer in an RFID (Radio Frequency Identification) system.
2. Description of the Related Art
In recent years, as an information management system for articles, an RFID system in which communication between a reader/writer and an RFID tag (also referred to as a wireless communication device) attached to an article is established using a noncontact method and predetermined information is transmitted has been used. As the RFID system, an HF band system in which a high-frequency wave of 13 MHz band is utilized and a UHF band system in which a high-frequency wave of 900 MHz band is utilized are typical examples. In particular, since a communication area is wide and it is possible to collectively read or write a plurality of RFID tags, the UHF band system has drawn attention.
As an RFID tag used for the UHF band system, for example, RFID tags described in Japanese Unexamined Patent Application Publication No. 2007-228437 and Japanese Unexamined Patent Application Publication No. 2007-295395 and equipped with dipole antennae are common. Each of these dipole antennae includes two radiation elements connected to a wireless IC chip, and a matching loop conductor connecting each of the radiation elements. The matching loop conductor is a conductor used to provide an inductance component to the wireless IC chip, and functions as a matching circuit that provides impedance matching between the wireless IC chip and the radiation element.
In recent years, RFID tags that are able to be directly attached to soft articles, such as clothes or gauze have been demanded. Naturally, such tags are required not only to be small and flexible but also to have high resistance to cleaning or folding.
However, such a dipole antenna of the related art as described in Japanese Unexamined Patent Application Publication No. 2007-228437 or Japanese Unexamined Patent Application Publication No. 2007-295395 requires a loop portion defined by a conductor pattern having a narrow line width. Therefore, the dipole antenna of the related art has a problem in that when being attached to linen goods, a fold line is formed in the loop portion at the time of cleaning or folding, which results in disconnection at the fold line. In addition, when the radiation element includes a portion whose line width is narrow, disconnection tends to occur in the narrow portion in the same way.
Furthermore, typically, the wireless IC chip is mounted on a pad for mounting a chip, and the pad and the radiation element are connected to each other through a lead wiring line. Since the lead wiring line also has a narrow line width, the lead wiring line provides another source of disconnection. In particular, since the wireless IC chip includes a semiconductor substrate, such as silicon, when the RFID tag is folded or bent, a stress tends to be concentrated in the peripheral portion of the wireless IC chip, and particularly, in a joint portion between the wireless IC chip and the radiation element, and disconnection tends to occur in this joint portion.